k.jpg|thumb|240px|right|This cosmetics store has lighting levels over twice recommended levels]] Over-illumination is the presence of lighting intensity (illuminance) beyond that required for a specified activity. Over-illumination was commonly ignored between 1950 and 1995, especially in office and retail environments; only since then has the interior design community begun to reconsider this practice. The concept of over-illumination encompasses two separate but related concerns:

Use of more artificial illumination than required is expensive and energy-intensive. This includes consideration both of the appropriate level of illumination when spaces are in use, and when they are unoccupied.

Clinical studies show that excessive levels of artificial light produce annoyance and health effects in a large fraction of the population. These effects may depend on the spectrum of the light as well as the overall brightness.Lighting accounts for roughly 9% of U.S. residential electricity use and close to 40% of U.S. commercial building electricity use. Money and energy could be saved by, for example, turning off office building lights overnight, using natural light whenever possible, and taking full advantage of occupancy sensors or simply flipping manual light switches in unoccupied spaces. In response to these concerns, the design and architecture communities are making greater use of indirect sunlight in modern commercial buildings.

Production of glare is a de facto indication of over-illumination, since that causes optical processing conflicts and confusion to the brain in processing optical inputs.Over-illumination is sometimes grouped with unnatural spectra because negative health effects may result from the excess illumination, and also because certain artificial lights (such as fluorescent lamps) provide intense illumination in certain frequency bands, unlike daylight, whose spectral power distribution is fairly even over the visible spectrum. The most desirable spectrum is that of natural sunlight, which the body is attuned to and uses to set the circadian rhythms.Over-illumination can contribute to light pollution, where stray light illuminates the outdoors or others' property in an unwanted way. Over-illumination is a topic normally addressed in the process of building design, whereas light pollution is normally addressed by zoning regulations."Over-illumination" generally does not refer to the extreme conditions of snowblindness or arc eye, in which ultraviolet light can induce physical damage to the cornea.

Lighting unoccupied areas is a significant waste of energy. Many office buildings are illuminated overnight and on weekends. In some cases, this is so that janitors working overnight do not have to bother turning lights on and off. Lighting of unoccupied areas can be reduced by installation of occupancy sensors or timers. Energy can also be wasted by operating outdoor lighting during daylight. In many cases this arises because the lights are controlled by timers, which must be reset periodically as the times of sunset and sunrise vary throughout the year.Retail stores, especially those with large windows, are sometimes illuminated overnight as a measure of crime prevention. The idea is that, with the lights on, burglars are visible from the outside and can raise an alarm.

Forsaking use of sunlight is often a design decision made by the architect or their subcontractor. Overlooking opportunities for skylights can be an issue with many building designs, but lack of coordination of interior light banks with indirect sunlight is even more common. At a minimum, the building design should offer sufficient independent light banks so that building occupants may select the most suitable combination of natural to augmented light. Very frequently entire floors of office buildings are designed with only one switch, so that perimeter areas near natural light are illuminated with the same level of artificial light as the dimmest interior zones. This lack of independent controls also would require an entire office floor of say to be fully illuminated if one office worker stays late for evening work. This can occur with even the most eminent of architects. Frank Lloyd Wright designed Marin County Civic Center in 1957 with only one or two switches serving very large office pools. This reportedly costs Marin County several thousand dollars per year in electricity costs.

Occupancy sensors are used primarily for bathrooms, conference rooms and storage areas. This is an energy waste issue and not a health issue. The payback time of most occupancy sensors is in the range of two to five years, and yet first-cost economics prevent the installation of occupancy sensors in the majority of cases where they would save energy and lighting maintenance costs.

Having too many lamps or not using available lighting controls is a common issue associated with over-illuminated buildings. Many instances of "designed in" over-illumination can be corrected by building managers without particular difficulty. In many instances over-illumination can be solved by removing a fraction of the lights or fixtures from a ceiling lighting system. In other cases a lighting retrofit can be conducted to replace older, less energy efficient fixtures with newer ones. Lighting retrofits can also be designed to reduce over-illumination; retrofits have typical payback periods of two to four years. In simpler cases many fluorescent ceiling illumination systems have multiple switch settings that allow tuning of the light intensity delivered, the most common version of this control being the "three-level switch", also called A/B switching. Much of the benefit of the excess illumination reduction comes from a better ratio of natural light to fluorescent light that can result from any of the above changes. Research has been conducted showing worker productivity gains in settings where each worker selects his or her own lighting level.

Health effects of over-illumination or improper spectral composition of light include increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety. Not only does bright light induce headache, but certain spectral distributions can increase the incidence of headache.Fatigue is a common complaint from individuals exposed to over-illumination, especially with fluorescent media. Some studies have shown that the flicker and over-illumination combined in some fluorescent systems yield particularly high fatigue incidence. Research on circadian rhythm in humans indicates that one reason for fatigue stems from the incorrect color spectrum of fluorescent light. Stress and anxiety are frequent outcomes from working in a setting of intense (especially fluorescent) lighting. Research has shown that annoyance from bright light leads to medical stress. It is clear that brighter, less spectrally correct light induces clinically measurable stress, The annoyance with purely artificial light and preference by office workers for natural light has been demonstrated by a number of studies spanning eastern and western cultures. Fluorescent lighting has also been linked to aggravating other psychological disorders such as agoraphobia.

Hypertension effects of over-illumination can lead to aggravation of cardiovascular disease and erectile dysfunction, which impacts are outcomes of long term cumulative exposure and associated systematic increases in blood pressure. The mechanism of this effect seems to be stress by related upregulation of adrenaline production akin to the fight-or-flight response. Not only does this result in fatigue, but also immuno-suppressive behavior that has been shown to be linked to increased cancers. The research indicates that increasing the ratio of natural light to artificial solves much of the problem, provided the total illumination level is not driven excessively high. Many of these health impacts may be primarily due to the spectrum of the light rather than the overall level of illumination, but more research is required to establish this.

Excessive energy use is often tolerated because the person who bears the cost is not the one making day to day decisions about lighting. Building managers and not building owners usually structure such things as janitorial use of lighting, setting or installation of timers, or the choice of lighting fixtures. Another contributor is a leasing structure, common in the U.S., where the tenant pays none of the electricity costs.There are also myths which continue to propagate, including better lighting decisions. One such is the idea that it costs more to turn fluorescent lighting off and on again than to keep it running. According to the U.S. Department of Energy, the amount of electricity consumed in lighting up a fluorescent lamp is equal to a few seconds or less of normal operation. Another myth is that more light is better, which is contradicted by health data.Architectural design can identify technological aspects of window design where window angles can be calculated to minimize interior glare and reduce interior over-illumination, while at the same time reducing solar heat loading and subsequent demand for air conditioning as energy conservation techniques. For the Dakin Building in Brisbane, California the angled window projections effectively provide permanent sunscreens, obviating interior blinds or shades.

Building automation and lighting control solutions are now available to help reduce energy usage and cost by eliminating over-illumination. These solutions provide centralized control of all lighting within a home or commercial building, allowing easy implementation of scheduling, occupancy control, daylight harvesting and more. Many systems also support demand response and will automatically dim or turn off lights to take advantage of DR incentives and cost savings. Many newer control systems are using wireless mesh open standards (such as ZigBee), which provides benefits including easier installation (no need to run control wires) and interoperability with other standards-based building control systems (e.g. security).

Energy conservation

Christmas lights

Daylight harvesting

Hypertension

Light pollution

Light sensitivity

Seasonal affective disorder

World energy resources and consumption

Visual comfort probability